Apparatus and method for selectively discharging the photoconductive surface of an electrostatic drum copier to facilitate the cleaning thereof

ABSTRACT

In a copying machine characterized in that a charging device, an exposure device, a development device, a transferring device for transferring the developed image to a transfer medium such as paper, a cleaning device and a discharging device are provided around a photoconductive drum in the foregoing order, the improvement comprising means for introducing a discharging light disposed next to the charging device, and a shutter which intercepts the discharging light for a time corresponding to the length of the transfer medium only when the transfer medium enters the body of the copying machine.

United States Patent [1 1 Fujitsuka et al.

APPARATUS AND METHOD FOR SELECTIVELY DISCHARGING THE PHOTOCONDUCTIVE SURFACE OF AN ELECTROSTATIC DRUM COPIER TO FACILITATE THE CLEANING THEREOF Inventors: Kaoru Fujitsuka, Oomiya; K0

Honda, lwatsuki, Saitama, both of Japan Assignee: Fuji Xerox Co., Ltd., Tokyo, Japan Filed: Dec. 22, 1972 Appl. No.: 317,779

Foreign Application Priority Data Dec. 27, 1971 Japan 46/105483 US. Cl. 355/15, 96/1 C, 355/14, 355/17 Int. Cl G03g 15/00 Field of Search 355/15, 14, 17, 3; 96/1 C Dec. 11, 1973 [56] References Cited UNITED STATES PATENTS 3,540,806 11/1970 Starkweather 355/3 R 3,318,698 5/1967 Schwertz 96/].1 3,698,926 10/1972 Furuichi 355/17 Primary Examiner-Richard L. Moses Att0rneyGerald J. Ferguson, Jr. et al.

[57] ABSTRACT In a copying machine characterized in that a charging device, an exposure device, a development device, a transferring device for transferring the developed image to a transfer medium such as paper, a cleaning device and a discharging device are provided around a photoconductive drum in the foregoing order, the improvement comprising means for introducing a discharging light disposed next to the charging device, and a shutter which intercepts the discharging light for a time corresponding to the length of the transfer medium only when the transfer medium enters the body of the copying machine.

6 Claims, 4 Drawing Figures PATENTED 1 3, 7 7 8, 148

FIG.4

APPARATUS AND METHOD FOR SELECTIVELY DISCHARGING THE PHOTOCONDUCTIVE SURFACE OF AN ELECTROSTATIC DRUM COPIER 'I-O FACILITATE TII'E CLEANING THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a copying machine and method, more particularly to a copying machine which has a discharging device for extinguishing unnecessary part of a latent image before development of the latent image electrosta'tically formed in an electrostatic copying machine.

2. Description of the Prior Art In electrostatic copying machines employing an electrostatic recording process represented by xerography, a powder image is formed in a photoconductive material and the powder image is transferred to a transferring medium represented by ordinary paper, and the transferred image is fixed thereon to obtain a copy of the original. In order to automatically perform these steps, a drum-like photoconductive material is used and around the drum are implemented the followin steps in the order shown in FIG. 1 that is:

1. Charging step aziln this step, a photoconductive drum 1 is uniformly charged to plus or minus polarity by use of a charging device or corotron 2.

2. Exposure step b: In this step, a light image is projected through an exposure device 3. onto the photoconductive drum 1 bearing the uniformly distributed charges which were deposited thereon by during previous charging step 0, thereby extinguishing charges at those portions where the light impinges to form a latent image according to the light image.

3. Development step c: In this step, developer consisting of colored powder termined toner and particles termed carrier is flowed onto the latent image by means of a development device 4, thereby causing the toner to stick to the latent image and make it visible.

4. Transferring step d: In this step, the toner image on the photoconductive drum 1 made during the development step c is transferred'toa transfer medium P such as a paper sheet by means of a transferring device or corotron 5 which includes means for charging the back surface of the transfer medium P to the same polarity as that of the charge formed during the charging step a.

5. Preliminary cleaning step e: In this step, the attrative force of thetoner to the charge on the photoconductive drum 1 is weakenedto faclitate the drum cleaning of the nextstep. A preliminary cleaning device 6 such as an A.C. or DC. corotron of the opposite polarity to that used in charging step a is employed.

6. Cleaning stepf: lnthis step, thetoner remaining'on the photoconductive drum 1 is removed by means ofa cleaning device 7'such as a brush which removes the toner and cleans the photoconductive drum surface, thus preparing the drum for the subsequent copycycle.

7. Discharging step g: In this step, electrostatic charges remaining on the photoconductive drum 1 are extinguished or eliminated by use of a discharging device 8 such as a lamp, and thus an electrically clean photoconductive drum surface is provided for the subsequent copy cycle.

By repeating the above steps witheach rotation of the photoconductive drum '1, a desired number ofcopies may be obtained. However, in cases where the toner image formed by the steps up to the development step c is not transferred in the transferring step d for some reason, much toner is left for the cleaning step f and accordingly it happens that the toner is not sufficiently removed by the cleaning step and is left on the drum for the subsequent copy cycle. Instances in which the transferring step d is not carried out occur, for example, when the transfer medium or paper P does not reach the transfer device 5 due to a paper jam or when the size of the transfer medium P is small in comparison with the size of the image formed on the photoconductive photosensitive drum 1. If the toner is left on the drum for the subsequent copy cycle as mentioned above, the remaining toner badly influences the quality of the copy made in the subsequent cycle and appears as a residual image in the reproduced image. Further, in a copying machine in which a chain gripper is used for feedng papers, it is desired that there be no image on the photoconductive drum at the position corresponding to the grippers at the time of transfer.

SUMMARY OF THE INVENTION Ths invention has been made in view of the abovementioned problems and has an object to provide a copying machine which has means for developing latent images only when required for transfer.

In summary, this invention includes a discharging means such as a light source which continuously irradiates the drum. This discharging step occurs after the charging step. The discharging is interrupted with a shutter, for example, when the transfer medium enters the body of the copying machine, the length of the interruption corresponding to the detected length of the transferring medium whereby a latent image may be formed and developed as discussed hereinbefore.

Other objects and advantages of this invention will become apparent upon reading the appended claims in conjunction with the following detailed description and the attached drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of a conventional copying machine.

FIG. 2 is an illustrative schematic view of a copying machine in accordance with the present invention.

FIGS. 3 and 4 are illustrative schematic, shutter operating circuits in acopying machine in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, a charging device 2, an exposure device 3, a developement device 4, transferring device 5, a preliminary cleaning device 6, a cleaning device 7 and a discharging device or lamp 8 are arranged around a photoconductive photosensitive drum 1 as in a conventional copying machine. Some of the light 9 from a discharge lamp 8 is irradiated on the photosensitive drum 1 by way of a mirror 10 and an exposure slit ll of the exposure device 3. Optionally, the mirror 10 may be replaced by an additional discharge lamp (not shown). This additional. discharge lamp would correspond to the light portion 9 and the additional discharge lamp will hereinafter be termed lamp 9. In this case, there would be no opening in the side of the enclosure for discharge lamp 8.

In the optical path of the discharge lamp 9 is provided a shutter 12 for intercepting or releasing the light, the shutter 12 being operated by energization of a soleniod 13. Whenever the optical path of the discharge lamp 9 is opened by the shutter 12, the charges produced by charging device 2 are extinguished by the discharging light even if the photoconductive photosensitive drum 1 has been exposed. Thus, the light from discharge lamp 9 may be directed onto the drum 1 anywhere between the charging device 2 and the developing device 4 although, for purposes of illustration, the light is directed in the exposure slit ll of the exposure device 3 in FIG. 2. Therefore, there is no fear that toner will stick to the drum surface by the subsequent development device 4.

Referring to FIG. 3, a paper sensing switch 14 may be provided in a passage (not shown) in the copying machine for the transfer medium. The switch 14 may be connected with solenoid 13. Thus, a transfer medium fed in the passage closes the paper sensing switch 14, and the solenoid 13 is energized thereby operating the shutter 12 and intercepting the light from the discharge lamp 9. When the rear end of the medium passes the paper sensing switch 14 and the switch 14 is opened, the solenoid 13 is deenergized and the shutter 12 is released so that the light from discharge lamp 9 is again radiated onto the photoconductive drum 1. Thus, the shutter 12 intercepts the light of the discharge lamp 9 for a length of time at least as long as the time corresponding to the length of the transfer medium. Accordingly, a latent image may be formed by exposure device 3 during this time.

Whenever it is desirable to delay the formation on the image on the drum such as by the length of a gripper (not shown) in acopying machine wherein the transfer medium is fed by means of a chain gripper, two paper sensing switches 14a and 14b are provided as shown in FIG. 4 with a proper distance therebetween equivalent to the length of the gripper. By such an arrangement, the shutter 12 is not operated until the gripper closes the second paper sensing switch 14b and thus unnecessary image formation can be avoided for the length of the gripper.

Since the shutter operates to intercept the light of the discharging device only during the time corresponding to the length, only images having a length corresponding to the length of the transfer medium are formed and no image is formed when the transfer medium does not come into the body of the copying machine because of accidents such as jamming of papers. Therefore, the cleaning device is only required to remove a small amount of residual toner. Further, the quality of the copy is improved, the interior of the machine is kept clean and the consumption of the toner is decreased.

Numerous modifications of the invention will become apparent to one of ordinary skill in the art upon reading the foregoing disclosure. During such a reading it will be evident that this invention provides copying method and apparatus for accomplishing the objects and advantages hereinstated.

What is claimed is:

1. In a copying machine comprising a charging device, an exposure device, a development device, a transferring device for transferring the developed image to a' transfer medium, a cleaningdevice and a discharging device disposed around a photoconductive drum in the foregoing order, the improvement comprising means for introducing a discharging light onto the photoconductive drum between the charging device and the development device, and shutter means for intercepting the discharging light for a length of time corresponding to the length of the transfer medium only after the transfer medium enters the body of the copying machine.

2. In a repetitive copying process used in a copying machine comprising the steps of charging a photoconductive member, posing the charged photoconductive member to an image to be copied to form a latent image, developing the latent image with a developer, transferring the developed image to a transfer medium, and cleaning the photoconductive member of residual developer and charge for the next cycle, the improvement comprising:

continuously removing the charge placed on said photoconductive member during said charging step and interrupting the continuous charge removal only after a said transfer medium has entered the body of the copying machine, the length of said interruption being approximately the length of time required for said developed image to be transferred to said transfer medium during said transfer step whereby the latent image may be formed on said photoconductive member during said interruption so that said developer is placed on said photoconductive member only for a length of time approximately as long as the interruption,

whereby developer is not placed on said photoconductive member whenever it is not necessary to transfer developer to the transfer medium so that residual developer on said photoconductive member is substantially removed during said cleaning step to thereby clean the photoconductive member for the next cycle of copying.

3. The improvement as in claim 2 where said charge is continuously removed by exposing said photoconductive member to light from a discharge lamp.

4. The improvement as in claim 2 where a discharge lamp is used in said cleaning step to remove said residual charge and where a portion of the light from said discharge means is used to effect said continuous charge removal.

5. The impovement as in claim 2, the length of said interrupting step is effected by sensing the length of time it takes for said transfer medium to pass a first predetermined point after it has entered the body of said copying machine.

6. The improvement as in claim 5 where said interrupting step is delayed a predetermined length of time by sensing the length of time it takes for said transfer medium to reach a second predetermined point subsequent to said first predetermined point. 

1. In a copying machine comprising a charging device, an exposure device, a development device, a transferring device for transferring the developed image to a transfer medium, a cleaning device and a discharging device disposed around a photoconductive drum in the foregoing order, the improvement comprising means for introducing a discharging light onto the photoconductive drum between the charging device and the development device, and shutter means for intercepting the discharging light for a length of time corresponding to the length of the transfer medium only after the transfer medium enters the body of the copying machine.
 2. In a repetitive copying process used in a copying machine comprising the steps of charging a photoconductive member, posing the charged photoconductive member to an image to be copied to form a latent image, developing the latent image with a developer, transferring the developed image to a transfer medium, and cleaning the photoconductive member of residual developer and charge for the next cycle, the improvement comprising: continuously removing the charge placed on said photoconductive member during said charging step and interrupting the continuous charge removal only after a said transfer medium has entered the body of the copying machine, the length of said interruption being approximately the length of time required for said developed image to be transferred to said transfer medium during said transfer step whereby the latent image may be formed on said photoconductive member during said interruption so that said developer is placed on said photoconductive member only for a length of time approximately as long as the interruption, whereby developer is not placed on said photoconductive member whenever it is not necessary to transfer developer to the transfer medium so that residual developer on said photoconductive member is substantially removed during said cleaning step to thereby clean the photoconductive member for the next cycle of copying.
 3. The improvement as in claim 2 where said charge is continuously removed by exposing said photoconductive member to light from a discharge lamp.
 4. The improvement as in claim 2 where a discharge lamp is used in said cleaning step to remove said residual charge and where a portion of the light from said discharge means is used to effect said continuous charge removal.
 5. The impovement as in claim 2, the length of said interrupting step is effected by sensing the length of time it takes for said transfer medium to pass a first predetermined point after it has entered the body of said copying machine.
 6. The improvement as in claim 5 where said interrupting step is delayed a predetermined length of time by sensing the length of time it takes for said transfer medium to reach a second predetermined point subsequent to said first predetermined point. 